The UN system is often referred to as a "family" of organizations. The charter of the UN, signed in San Francisco on 26 June 1945, defined six main organs of the new world body, each with specific tasks and functions.

The League of Nations grew out of the catastrophe of World War I (1914–18). Though the idea of the establishment of a body in which the nations of the world could settle their disagreements had been put forth periodically since antiquity, the League, created at the 1919 Paris Peace Conference, was the first organization of sovereign states designed to be universal and devoted to the settlement of disputes and the prevention of war.

The creation of the UN at the San Francisco Conference in June 1945 was the culmination of four years of concentrated preparation. During these years, the idea of a world organization to replace the League of Nations was first debated and then fleshed out.

As of November 2002, the UN had 191 member states, including 51 charter members (the 50 countries that sent representatives to the San Francisco conference, plus Poland, which ratified the charter shortly afterward) and 140 states that have joined the organization since 1945, the great majority of them former colonial territories that have achieved independence. The table in this chapter shows the growth of UN membership, the roster lists the members of the UN in alphabetical order and gives the dates of their admission to the UN.

Under the Charter, it is the task of the General Assembly to "consider and approve the budget of the Organization" and to apportion the expenses of the UN among the member nations. From an administrative standpoint, the expenditures of the UN may be said to fall into two categories: expenditures that are included in what is termed the "regular budget," to which all members are obliged to contribute; and expenditures for certain high-cost items or programs, for which are established separate, or "extrabudgetary," accounts or funds financed by special arrangements that do not necessarily involve obligatory payments by UN members.

Under the charter, the members of the UN vest in the Security Council primary responsibility for maintaining international peace and security. To facilitate its work and to ensure quick and effective action when required, the council has certain powers and attributes not accorded the other organs of the UN.

Unlike the other main organs of the UN, the Trusteeship Council was established for the purpose of executing a closely defined system of operations. This is the trusteeship system, which was devised to adapt the League of Nations mandate system to meet the requirements of a new era.

The International Court of Justice was established at the San Francisco Conference in 1945. It is a successor to and resembles the Permanent Court of International Justice created at the time of the League of Nations, but its competence is wider, because membership in the League did not automatically require a nation to join the Permanent Court.

The charter lays down very few requirements governing the establishment of the sixth main organ of the UN—the Secretariat. Such requirements as are specified, in Chapter XV, may be conveniently listed under the following headings.

From the outset, the secretary-general of the UN has played an important role in helping to settle crises that have troubled nations since the end of World War II. In practice, the role has gone far beyond what might be anticipated from a reading of the terse Charter provisions for the office.

The first purpose of the UN, as stated in Article 1 of its charter, is the maintenance of international peace and security. To this end, the organization is required "to take effective collective measures for the prevention and removal of threats to the peace, and for the suppression of acts of aggression or other breaches of the peace, and to bring about by peaceful means … adjustment or settlement of international disputes or situations which might lead to a breach of the peace." The UN has undertaken this heavy responsibility with varying levels of success over the years.

The earth is essentially a liquid planet, with more than 70% of its surface covered by water. Although geographically divided and labeled as continents, islands, seas, and oceans, the earth, when viewed from outer space, appears as one large body of water interspersed with lesser land masses.

Article 55 of the charter, on international economic and social cooperation, calls on the UN to promote higher standards of living, full employment, and conditions of economic and social progress and development. The fostering of economic and social development, however, was only one of several objectives specified in the charter, and no special emphasis was accorded to it.

The International Development Strategy for the third UN Development Decade called for a renewed emphasis on technical cooperation and a significant increase in the resources provided for this purpose. It recognized that technical cooperation contributes to the efforts of developing countries to achieve self-reliance by facilitating and supporting investment, research, and training, among other things.

International disaster relief, the special problems of children, refugees, the elderly, youth, the disabled, and families are all subjects for which member states have directed the UN to provide international leadership and expert guidance. The global nature of trade in illicit narcotic drugs and the internationalization of criminal activities were social ills that became so destabilizing at the end of the twentieth century that member states requested their international organization to implement innovative global programs to maintain security and social justice.

In the Preamble to the Charter, "the peoples of the United Nations" express their determination "to reaffirm faith in fundamental human rights, in the dignity and worth of the human person, in the equal rights of men and women and of nations large and small." Article 1 of the Charter states that one of the purposes of the UN is to promote and encourage "respect for human rights and for fundamental freedoms for all without distinction as to race, sex, language, or religion." In Article 56, "all Members pledge themselves to take joint and separate action in cooperation with the Organization for the achievement" of this purpose. The Charter vests responsibility for assisting in the realization of human rights and fundamental freedoms in three of the principal organs: the General Assembly, the Economic and Social Council, and the Trusteeship Council.

Since the creation of the UN, more than 80 territories that were formerly under foreign rule have become sovereign states and members of the UN. In this radical transformation of the world's political map, the UN has played a significant role that stems from the basic precepts of its charter as laid down in Article 1, which states that one of the purposes of the UN is to "develop friendly relations among nations based on respect for the principle of equal rights and self-determination of peoples, …" Chapters XI, XII, and XIII of the charter are devoted specifically to measures that are designed to promote the welfare of dependent peoples.

The idea of developing international law through the restatement of existing rules is not of recent origin. In the last quarter of the eighteenth century, Jeremy Bentham proposed a codification of the whole of international law.

On 10 December 1948 the General Assembly of the United Nations adopted and proclaimed the Universal Declaration of Human Rights. Following this act, the Assembly called upon all member countries to publicize the text of the Declaration and "to cause it to be disseminated, displayed, read and expounded principally in schools and other educational institutions, without distinction based on the political status of countries or territories." The full text of the final authorized version follows.

Readers with access to a computer and modem can access online sources of information about the United Nations via the internet. Current United Nations press releases, resolutions, and documents and breaking information on the UN's international conferences are maintained on the Internet at www.un.org/News.